Narrow Results

We discuss the physical applicability of a model for a class of compact stars, employing Vaidya–Tikekar¹² geometry of space–time. It is shown that the model can generate an equation of state (EOS) very similar to the one obtained by earlier workers for SAX J1808.4-3658 (SAX in short), assumed to be a strange star. The stellar configuration, as described by the model, is shown to be stable under radial perturbations. This may explain why the star SAX is known to be very stable compared to other low mass binary X-ray emitters.

Employing the Quark Mass Density- and temperature-dependent model and the Hartle's method, we have studied the slowly rotating strange star with uniform angular velocity. The mass–radius relation, the moment of inertia and the frame dragging for different frequencies are given. We found that we cannot use the strange star to solve the challenges of Stella and Vietri for the horizontal branch oscillations and the moment of inertia I₄₅/(M/M_s)>2.3. Furthermore, we extended the Hartle's method to study the differential rotating strange star and found that the differential rotation is an effective way to get massive strange star.

We calculate the maximum mass of the class of compact stars described by the Vaidya–Tikekar²⁷ model. The model permits a simple method of systematically fixing bounds on the maximum possible mass of cold compact stars with a given value of radius or central density or surface density. The relevant equations of state are also determined. Although simple, the model is capable of describing the general features of the recently observed very compact stars. For the calculation, no prior knowledge of the equation of state (EOS) is required. This is in contrast to earlier calculations for maximum mass which were done by choosing first the relevant EOSs and using those to solve the TOV equation with appropriate boundary conditions. The bounds obtained by us are comparable and, in some cases, more restrictive than the earlier results.

Previous research studies observed that quark mass scalings typically neglect the inclusion of asymptotic freedom. However, we have introduced a Woods–Saxon-like factor to incorporate the effects of asymptotic freedom into our new mass scaling. Our findings indicate that the equation of state and sound velocity for strange quark matter exhibit different behaviors at zero temperature when using this new mass scaling. This suggests the presence of novel properties in the phase transition and structure of strange stars. Additionally, through numerical calculations, we have successfully obtained a strange star with a mass two times that of the Sun, aligning with astronomical observations. In a parameter group considering first-order perturbation effects, characterized by large C and small D, we have made an interesting discovery: the surface density of the strange star can be lower than that of normal nuclear matter. This observation serves as a possible signal of a phase transition from quark matter to nuclear matter.

This study investigated the formation and evolution of a strange star known as SAX.J1808.4–3658 in the Krori–Barua Rainbow spacetime, resulting from the collapse of string fluid. The study examined the dynamical variables derived from the field equations, taking into consideration the influence of the particle’s energy on the mass density, pressure, and string tension. Additionally, various techniques were employed to analyze the physical properties, including gradients, energy conditions, anisotropy, stability, the Tolman–Oppenheimer–Volkoff equation, mass function, compactness, and red-shift. The study’s findings revealed that the strange star SAX.J1808.4–3658 satisfies all the conditions necessary for its evolution from an anisotropic string fluid. This discovery suggests that strange stars might have emerged during the string-oriented quark era of the Universe. The researchers presented all the physical quantities within the frameworks of both rainbow gravity and general relativity, while also utilizing graphical representations to aid in comprehending the study’s findings. The energy conditions and anisotropy were found to be fulfilled, indicating the stability of the strange star. Furthermore, the Tolman–Oppenheimer–Volkoff equation was employed to determine the maximum mass of the strange star, which was found to align with observational data.

In this paper, we have developed a class of new solutions for relativistic compact stars in higher-dimensional $(D\ge 4)$ space-time assuming pseudo-spheroidal geometry of the $g_{rr}$ metric component. To study the physical properties, we consider equation of state of interior strange matter $p=\frac{1}{3}(\rho -4B)$, as proposed in MIT bag model in the presence of a density-dependent $B$ parameter. The interior matter of a quark star may consist of three flavor quarks. We observe some interesting results. The parameter $B$ depends on the anisotropy $(\alpha )$ in the interior, and at the stellar surface, $B$ attains a constant value independent of $\alpha$. At the interior, $B$ increases with the increase of $\alpha$. We also note that the value of B approaches a constant value with increasing spheroidal parameter $\lambda$. $B(\rho )$ also depends on space-time dimensions and it is interesting to note that $B(\rho )$ picks up negative values near core region which limits the number of space-time dimensions available for a stellar model. All the stability criterion and energy conditions hold good for a physically realistic stellar configuration. It is observed that strange quark matter may be stable or metastable or unstable depending upon the value of energy per baryon $(E_B)$. Strange quark matter will be stable if energy per baryon $E_B<930.4{\mathrm{\text{MeV/fm}}}^3$. It is noted that the maximum mass obtainable in this model is $1.99M_{\odot }$ considering stable strange quark matter when dimension $D=4$. In addition, we observe that the dimensions have some effect on the gross properties of strange stars (SS).